Bølling-Allerød Productivity in the Subarctic Pacific Driven by Seasonal Upwelling

The Bølling-Allerød deglacial event is marked by high diatom productivity and opal deposition throughout the subarctic Pacific. This opal could either constitute a strengthened biological pump and thus carbon sequestration, or a weakened biological pump and release of marine-sequestered CO₂ to the atmosphere. We quantify silicic acid supply at IODP Site U1340 in the Bering Sea using biogenic opal and δ³⁰Si of Coscinodiscus, a diatom genus. These records, along with diatom environmental indicators, suggest the Bølling-Allerød had high silicic acid availability related to a shift from stratification to seasonal upwelling dynamics. We thus propose the primary cause of the high productivity event was increased macronutrient supply from vertical exchange that injected old, nutrient-rich, CO₂-rich waters into the surface. Enhanced CO₂ release from the subarctic Pacific may help explain critical intervals of CO₂ rise that occur at the onsets of the Bølling-Allerød and PreBoreal.